CA1324570C - Method for blanking thin sheets, and in particular metal sheets and elastomeric material of utility for said method - Google Patents

Abstract

METHOD FOR BLANKING THIN SHEETS, AND IN
PARTICULAR METAL SHEETS AND ELASTOMERIC MATERIAL
OF UTILITY FOR SAID METHOD

ABSTRACT
A punch construction which cooperates with a die for blanking an edge of a sheet of sheet material is disclosed.
The punch construction comprises a heterogeneous elastic material having alternating regions having a relatively higher hardness and complimentary regions having a relatively lower hardness.
The construction provides a blanking which is cheaper than known blanking methods and yet avoids the formation of burrs.

Description

1 3 2 4 ~ 7 0 20497-590D

METHOD FOR BLANKING THIN SHEETS, AND IM
PARTICULAR METAL SHEETS AND ELASTOMERIC MATERIAL
OF UTILITY FOR SAID METHOD

This is a divisional application of application Serial No. 567,456 filed on May 20, 1988.
The parent application relates to a method and apparatus for blanking material in ~he form of a relatively thin sheet of any material, and in particular a thin metal or non-metal sheet.
This application relates to a punch construction which cooperates wlth a die for blanking an edge of a sheet of sheet material.
It should be noted that the term "invention" appearing in the specification applies to the subject matter of both the parent and the divisional applications.
The blanking out along an open or closed perimeter of sheet stock is effected on a blanking press comprising essentially a movable ram carrying a punch having a shape corresponding to the perimeter to be blanked and a fixed table on which rests the blanking die having the conjugate shape cooperating with the punch to form the desired blank.
The punoh and the die are usually of metal and in ; particular made from tool steel for blanking metal sheets.
One of the major drawbacks of this technique resides in the necessity to adjust the operational clearances between ~:
the die and the punch w1th high precision in order to avoid burrs. It is ~ndeed considered in practice that the allowable .. .. ~ ,, , ~ 3 2 4 ~ 7 0 20497-590D
clearance must not be more than one-tenth of the thickness of the part to be blanked. It is therefore obvious that this tolerance is extremely difficult to conform to in industrial plants, or at least at acceptable costs for extra-thin sheets having a thickness less than 0.5 mm. Moreover, the maintenance cost increases with decrease in the allowable tolerances.
The abject of the present invention is to overcome these drawbacks by providing a blanking method which is cheaper and yet avoids the problems of the formation of burrs.
The invention therefore provides a punch construction which cooperates with a die for blanking an edge of a sheet of sheet material, the punch constnlction comprising a heterogeneous elastic material having alternating regions having a relatively higher hardness and complimentary regions having a relatively lower hardness.
The heterogeneous composite elastic material is foxmed by an elastic mass having a given hardness including a structure composed of an elastic material having a different hardness defining a meshing for inducing differentiated stresses on the surface of the sheet to be blanked.
;~ According to a variant, the heterogeneous composite elastic material comprising in alternating relation regions , constituted by an elastomer contiguous to empty regions.
, According to another variant, the heterogeneous '~ composite elastic material i5 formed bv a hollow waffled structure having a given hardness defining cavities filled with a material having a different hardness.

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The waffled structure comprises on the whole of its surface opposed to the active working surface an elastic distributing mass.
According to other variants:
the hardness of the distributing mass is relatively low;
the waffled structure has closed cavities;

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:' ; : ' -1324~70 the waffled structure has open cavities communicating with the distributing mass the walls of the cavities are hard and the rest is ~oft.
According to another variant, the structure is embedded in the elastic mass and is constituted by a material having a given hardness de~ining a cros~ing network having a 9Ui-table meshing. This structure may be in particular in the form of a grilleor lattice.
The invention also concerns a heterogeneous composite elastic material of utility for carrying out the method de-fined hereinbefore. This material is in particular in the form of an elastic cushion.
Th~ material from which thi~ cushion i9 made may be in particular an elastomer such aq silicone polymer or an elastomeric polymer such as polyurethane. The heterogene-ous composite elastomeric material may be wrapped in an outer skin serving as a protection. t The method according to the invention is based on the fact that the heterogeneity or' the mass of ela~tic material enable~ the stresses to be concentrated along locali~ed nes corresponding to the coincidence of the regions of high hardness with the sharp edge of the die. This concen-tration initiates the blanking operation by cracking at the point of origin, fracture and propagation of the cut initiated by another heterogeneous region.
The elastomeric cushion i5 formed by a mass of material .

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~32~70 having a given hardness in which is embedded a material of higher hardness, for example in the form of a network o crossing vein~ defining a meshing similar to a grilleor grilling. In this case, the regions of relatively higher S hardness are included in the mass of the material having a relatively lower hardnes~.
According to a variant described hereinbefore wafl structure), the elastomeric cushion may be similar to a honeycomb structure whose cavities are filled with a mate-rial of relatively low hardness. The honeycomb structure,i.e. the alveolate structure, may be designed in isuch ~an-ner that the regions having a relatively higher hardness open onto or do not open onto the surface.
The heterogeneous structure maycomprise an elastic distri-lS buting mass, i.e. a distributing elastomeric sub-layer on the side facing the punch, transmitting the force ~ the~rto whole of the heterogeneous structure which is placed on the sheet, it~elf in contact with the sharp edges of the metal die defining the regions to be blanked.
As~eessential feature of the invention resides in the ~ alternation of regions o~ different hardnesses, the hard ,~ regions may be symmetrically reversed with the soft regions.
The following description, with reference to the ac-1~ companying drawings, will explain how the invention can be '1 25- carried out. In these drawings :
Fig. 1 is a diagrammatic elevational view of a conven-tional sheet blanking device ' :

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_ 5 -Fig. 2 is a diagrammatic sectional vi~w of a ~,heet blanklng device according to the invention , Fig. 3 is a partial top plan view of the punch of hete-rogenous composite elastomeric materiai according ~o the invention Fi7~,. 4 is a sectional view taken on line 4-4 of Fig.3 Fig. 5 is a partial per~pective view o ~he punch ac-cording to the invention , Figs. 6 and ;' are respectively partial sectional views of two variants of the alveolate struc~ure of the punch ;
~:Figs. 8 and 9 are respectively diagrammatic perspective views of two variants o~ the punch of a heterogeneou~ com-posite elastic material according to the invention ;~Figs. 1 0 to 13 illus,trate diagrammatlcally the pres~u-re induced by the press on a sheet and the di3tribution o~
~;the ~orces as a function of the punch according to the invention ;
Figs. 14 and 15 are respectively a section of the punch on a sheet and a corresponding diagram of the distribution of the stresses.
The conventional sheet blanking device shown in Fig. 1 -comprises a press which may be used for blanking a sheet 1.
This press comprises, on one hand, a movable ram 2 carrying the blank holder 3 and a punch 4 having a shape correspond-¦ 25 ing to the perimeter to be blanked out, and, on the other ~ hand, a fixed table 5 on which bears a die 6 having sharp '`f edges 7 having the conjugate shape cooperating with the ,3;
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' ` : - : . : , ~32~70 _ 6 --punch 4 for ohtaining a blanked out sheet 8.
The sheet blanking device according ~the invention shown in Fig. 2 is likewise a press which may be used for blanking out a sheet 1 and essentially comprising, in addi-tion to the die 6 having sharp edges 7, a mov~ble ram 2 carrying a punch 4.
The punch 4 i~ constituted by a heterogeneous elastic material having localized regions 4a having a relatively higher hardness and complementary regions 4b having a rela-tively lower hardness. This heterogeneous structure formlng a punch includes, on the side opposed ~o the active surface of the punch, an elastic distributing ma~s 9 which is a su~-layer of elastomer and which transmits the force of the punch to the whole of the heterogeneou3 structure which is placed on the sheet, the latter being in contact with the ~harp edges 7 of the metal die defining the regions to be blanked.
The materials from which the heterogeneous structure 4 and the distributing mass 9 are made may be in particular an elastomer such as a silicone polymer or an elastomeric polymer such as polyurethane.
As shown in Figs. 3 to 5, the heterogeneous composite elastic material constituting the punch 4 is similar to a waffled honeycomb structure defining a meshing and includ-ing a mass 4a of a material having a higher hardness in which are formed alveoles 4c filled with the material having a relatively lower hardness 4b. Consequently, the walls o the alveoles 4c are hard and the interior of the alveoles is soft.

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In order to show the shape of the alveoles 4c, there have been shown in Figs. 3 to 5 empty alveoles and filled alveoles, in this embodimentthe~eafthe ~veoles is filled with the relatively lower hardness material.
In these Figures, the alveoles 4c have the shape of a frustUm of a pyramid having six sides, but they may have another shape, for example a cylindrical shape or a rusto-conical shape.
This honeycomb structure, i.e. alveolate structure, may be so designed that the regiong 4b having a relatively lower hardness open onto or do not open onto the active surface, as shown respectivley in Figs. 4 and 6. The re-gions 4b having a relatively lower hardnes~ may also be in-cluded in the middle of the mass of the material 4a of rela-tively higher hardne~s (Fig. 7).
Furthermore, ~he waffled structure of the punch 4 mayhave closed alveoles 4c or open alveoles 4c communicating with the distributing mass 9.
These alveoles may also be empty so as to form a hete-rogeneous composite elastic material comprising an alterna-tion of regions formed by an elastomer contiguous to empty I region~.
According to a variant shown in Fig. 8, the heterogene-ous composite elastic material constituting the punch 4 has a waffled structure in the form of hollows also including regions having higher hardness lOa and regions having lower hardness lOb which define a crossing network having a .,~ .
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, ~324~70 suitable meshing. In this case, the regions lOb may be empty.
According to another variant shown in Fig. 9, the he-terogeneous composite elastic materlal con~tituting the punch 5 4 i9 formed by a mass llb of a material having a lower hard-ness in which are embedded regions lla having a higher hard-ness defining a meshing similar to a grill~or grilling.
The heterogeneity of the mass of elastic material orm-ing the punch 4 enables the stresses to be concentrated along localized lines 12, as diagrammatically shown in Fig.10 corresponding to the coincidence of the high hardness re-gions with the sharp edge 7 of the die 6.
Figs, 11 to 13 show that this concentration initiates the blanking operation by a cracking at the point o origin, fracture and propagation of the blanking operation by a shearing up to the meeting with another line of progression of the blanking operation initiated by another region of heterogeneity. More precisely, Fig. 11 shows the cracking by concentration of the stress of the sheet 1 against the sharp edge 7 of the die 6, Fig. 12 shows the blanking opera-tion on the sharp edge 7, and Fig. 13 the progression o~ the blanking operation by a shearing effect.
Fig. 14 shows the heterogeneous composite elastic mate-rial forming the punch 4 and including regions 4a of higher hardness and regions 4b of lower hardness on a sheet 1, while the corresponding Fig. 15 shows diagrammatically the distribution of the stresses exerted on the sheet 1 as a . ' .
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~324~70 g function of the regions 4a of higher hardness in the form of a diagram representing their variations.
As the essential feature of the invention resides in the alternation of the regions of different hardnesses , the hard regions and soft regions may be reversed.

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Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A punch construction which cooperates with a die for blanking an edge of a sheet of sheet material, the punch construction comprising a heterogeneous elastic material having alternating regions having a relatively higher hardness and complimentary regions having a relatively lower hardness.

2. The construction of claim 1 wherein said heterogeneous elastic material comprises an elastomer.

3. The construction of claim 2 wherein said elastomer comprises a silicone polymer.

4. The construction of claim 2 wherein said elastomer comprises an elastomeric polymer.

5. The construction of claim 2 wherein said elastomer comprises a polyurethane.

6. The construction of claim 1 wherein said punch further comprises a skin layer provided on said heterogeneous elastic material.

7. The construction of claim 1 wherein said heterogeneous elastic material comprises elastomeric regions and contiguous empty regions which alternate with each other.

8. The construction of claim 1 wherein said heterogeneous elastic material comprises waffled structure having a given hardness and defining alveoles filled with material of a different hardness.

9. The construction of claim 8 wherein said waffled structure includes a working surface facing said die and a back surface and wherein said punch construction further comprises an elastic distributing mass located adjacent said waffled structure back surface.

10. The construction of claim 8 wherein said waffled structure comprises closed alveoles.

11. The construction of claim 8 wherein said waffled structure comprises open alveoles.

12. The construction of claim 8 wherein said alveoles comprise relatively hard walls surrounding a relatively softer central portion.

13. The construction of claim 1 wherein said heterogeneous elastic material comprises an elastic mass having a given hardness and a mesh structure embedded in said elastic mass, said mesh structure comprising material of a different hardness than said elastic mass.